Method of making header dies



Oct. 7, 1958 l. A. SMITH 2,854,867

METHOD OF MAKING HEADER DIES Original Filed April 29, 1955 I 2Sheets-Sheet 2 INVENTOR ATTORNEYJ United States Patent METHOD OF MAKINGHEADER DIES Original application April 29, 1953, Serial No. 351,902.

Divided and this application March 7, 1955, Serial No. 492,664

6 Claims. (Cl. 76-107) The present invention relates to methods ofmaking header dies for cold heading machines, particularly relating todies for use in the heading of screws and the like. This application isa division of my co-pending application filed April 29, 1953, Serial No.351,902.

Threaded fasteners provided with heads, such as the conventional woodscrews, machine screws, etc., whether of the slotted head variety or ofthe Phillips head type, are produced in the form of an unthreaded headedblank which is then provided with threads by a thread rolling or threadcutting step. Conventionally, the blanks are produced by the coldheading method in which short lengths are severed from a coil ofsuitable wire stock, transferred to the header die, and subjected to oneor more sharp blows whereby the metal of one end of the short length ofwire is upset to form the required head. In manufacturing screws of thePhillips type, the headed blank is then subjected to a second blow,delivered by another punch which is suitably shaped to produce in thehead the desired tool receiving recess.

The header die is the cylindrically shaped tool in which the cut-offportion of wire is retained during the successive blows of the upsettingoperation. This die is often considered the most important header toolbecause it controls the finish, shape and dimensions of the headedblanks and its life is, indirectly, .a measure of the overall efliciencyof the header itself. The manufacture of header dies, in particular thefinishing operations, has long been something of a problem to the coldheading industry and has become particularly acute in heading precisioncountersunk head screw blanks for aircraft fasteners from alloy steel,because of the accuracy required and the difficulty of cold forming thealloy material.

Usually these dies are produced from a good grade of heading die steelby first cutting off from bar stock of the size required, drilling, andthen reaming, counter boring or otherwise machining to the approximatehole dimensions required. The dies are next heat treated and then mustundergo further reaming, grinding, lapping or honing of the internalhole to the finished dimensions in the hardened stage. While under idealcircumstances, any of these methods may provide relatively smooth holes,inherently there will be minute annular unevenness or inaccuracies withrespect to the hole. This condition occurs because of the necessity ofrotating the die or the cutting tool, or both, in performing any of theconventional finishing operations such as reaming, grinding, etc. Thisroughness offers a serious problem on dies for aircraft parts whichusually require extruding in the heading operations; that is, the wirediameter is reduced as it is pressed into the die when it meets thetapered portion commonly known as the extruding choke. Not only .wouldsuch annular roughness, however minute, reduce die life by exposing highpoints only to wear but it would restrict the flow of metal in extrudingand scrape the lubricant from the wire quickly leading to galling,chipping and ultimate die failure.

A primary object of the aforesaid co-pending application is theprovision of a die in which the aforesaid minute annular inaccuraciesare entirely absent, which die, therefore, has an increased useful life,during which the production of screw blanks of a higher quality isfacilitated. A primary object of the present application is theprovision of a suitable method for the manufacture of such dies.

More specifically, it is an object of the present invention to provide amethod of making a cold header die comprising a hardened steel bodyhaving a central aperture for receiving the material to be headed, saidaperture having a wall in which any irregularities extendlongitudinally. A feature of such dies is or may be a shallow annularconcavity which tends to prevent premature pulling out of the headedscrew blanks by the recess-forming punch. Another object is theprovision of a method of the character described, in which the apertureWall is compressed and work-hardened to a degree giving it a smooth,hard finish which not only facilitates performance of its function, butresults in the production of a better quality of screw blanks.

Another object is the provision of a method of making header dies of thecharacter described which method comprises the steps of preparing anunhardened die blank, supporting the die blank with one end and alllateral surfaces rigidly confined, and cold forming the die blank underheavy pressure with a hardened and polished hob having a configurationsubstantially complementary to the desired finished die, said hob havinga body and a cy1indrical projection, the latter penetrating the dieblank in the forming step to produce .a die aperture in which anyirregularities of the walls extend longitudinally. A subsidiary objectis the provision of such a method in which said forming is performedwith sufiicient pressure to cause annular elastic bulging of the hobprojection, whereby a shallow annular concavity is formed in the wall ofthe die aperture.

Other and further objects, features and advantages will be apparent fromthe description which follows, read in connection with the accompanyingdrawings in which:

Figure l is an axial section of a conventional cold header die of theprior art;

Figure 2 is a greatly enlarged fragmentary sectional view correspondingto the portion A of Figure 1;

Figure 3 is a view partly in section and partly in elevationillustrating the beginning of the forming step of the method accordingto the present invention;

Figure 4 is a view similar to Figure 3 illustrating the: furthestpenetration of the hob into the die blank;

Figure 5 is an axial section of a finished die according: to theinvention;

Figure 6 is a greatly enlarged fragmentary view corresponding to theportion B of Figure 5;

Figure 7 is a fragmentary axial section illustrating the die of Figure 5when in use in a cold heading machine;

Figures 8, 9, 10 and 11 are axial sections illustrating other forms ofheader dies which may conveniently be produced by the method of thepresent invention;

Figure 12 is an axial section illustrating a die blank after completionof the forming step according to the invention;

Figure 13 is a similar view showing the die blank of Figure 12 aftercompletion of a further step in the production of a die;

Figure 14 is a similar view illustrating another form of die;

Figure 15 is an axial section of a still further form of die producedaccording to the invention; and

Figure 16 is an enlarged fragmentary view corresponding to Figure 15.

In order to .facilitate an understanding of the invention, reference ismade to the embodiments thereof shown in the accompanying drawings anddetailed descriptive language is employed. It will nevertheless 'beunderstood .thatno limitation of the invention is thereby intended andthat .various changes and .aiterations are contemplated such as wouldordinarily occurxto one skilled in the art to which the inventionrelates.

A-typical header die of conventional form, as now in common use, isillustrated in Figures v1 and 2, the particular die shown being of theextrusion type. Such a die comprises .a cylindrical -:body of steelhaving a central aperture 11 extending therethrough. The aperture 11comprises ,a cylindrical portion 12, which may be defined-as a backholeor knock-out hole, .a tapered portion 13, a-short cylindricalportion 14 of smaller diameter than the portion 12, a short taperedportion 15, another cylindrical portion 16 of a diameter equal to thedesired shank diameter of the finished screw, and a flaring countersunkportion 17. A die of the form illustrated in Figure l is employed in themanufacture of countersunk head screws, and is termed an extrusion diesince the wire blank, upon being inserted from the front of the die(upper end in Figure 1) is, through a part of its length, forced pastthe constricted cylindrical portion 14, or extruding choke, reducingthediameter of that portion of the blank which is to be threaded. Inother words, after a blank has been headed in a die of the typeillustrated in Figure 1, the headed blank will conform to theconfiguration of the portions 17, 16, and 14 of the die, but the portionof the blank which has penetrated beyond the extruding choke 14 will, ofcourse, conform to that diameter throughout its length and, therefore,will not have the configuration of portions 12 and 13 of the die. Thecylindrical portion 12 of the aperture accommodates the usual knockoutpin for removing the headed blanks from .thedie after the completion ofthe heading operation on each blank.

Dies of the type illustrated in Figure l have heretofore beenmanufactured according to the technique described at the outset hereof,including the steps of drilling, reaming, counterboring, and heattreatment followed .byfurther reaming and then by grinding, lapping orhoning of theinternal hole to the finished dimensions. As stated, thispractice results necessarily in the formation of minute annularinaccuracies 13 which are shown in enlarged and somewhat exaggeratedform in Figure 2, such annular inaccuracies 18 resulting in thedisadvantages previously mentioned. Moreover, the involved andtime-consuming operations heretofore necessary for the production ofsuch dies greatly increases the cost thereof, many hours being requiredfor the production of each die.

On the contrary, by the method of the present invention, a better diecan be produced in a few minutes, resulting in a reduction in theproduction cost of the dies as well as providing dies which are bettersuited to the production of high quality screws and the like. Accordingto the invention, there is first produced a hob 19 (Figure 3) having acylindrical body 20 and a die-penetrating central projection comprisinga cylindrical terminal portion 21 of reduced diameter, an interveningtapered portion 22, an intermediate cylindrical portion 23 of slightlylarger diameter than that of the terminal portion '21, and a furthertapered portion 24 joining the portion 23 and the body 21 The portions21-24 are formed to produce portions 14, 15, 16 and 17 of the die asrequired. The hob is formed of hardened steel and is carefully machinedand finished to exact dimensions and a mirror finish. A hob as describedwill serve in the production of a considerable number of dies.

In forming the die a. length of bar stock of the required size isdrilled to produce a blank 25 having a central aperture 26 of slightlysmaller diameter than the projection 21 of the hob. The blank 25 is thenrigidly confined below .edmachinescrews or tapping screws.

and laterally, by means of an anvil (not shown) and a chuck orreceptacle 27, and the hob 19 is forced into the blank 25 under greatpressure until it has penetrated to the desired extent, as shown inFigure 4. In the performance of this step, the surface of the metalsurrounding the drilled aperture 26 of the die blank is compressed andwork-hardened, giving it a superior finish and hardness. The hob is thenwithdrawn from the die blank, and the die is completed by grinding orotherwise machining the front or upper surface thereof to the requiredextent.

in carrying out the cold forming or hobbing step as described, it willbe obvious that any minor irregularities which might possibly be formedin the internal surfaces of the die will extend longitudinally, ratherthan annularly, and will not, therefore, have any adverse effect uponthe die or the screw blanks produced by its use. A further advantage ofthe present method resides in the fact that .in some cases, for exampleinthe productionof an extruding die 30 such as illustrated in Figure 5by the method described above and illustrated in Figures 3 and .4, theportion .23 of the hob, being .of somewhat greater diameter than theportion 21 which itself is of larger diameter than the drilled hole 26,naturally encounters very great resistance in penetrating the die blank.As a result of such resistance, and the considerable pressure used inthe process, the portion 23 of the hob is elastically deformed by theformation of a shallow annular bulge at its lower end, adjoining thetapered portion 22. This results in the formation of a correspondingshallow annular recess in the die 30, best illustrated in Figure 6,Wh816- in the annular recess 31 is shown greatly enlarged and somewhatexaggerated. The presence of such shallow annular recess is of advantagein the heading of short header point screw blanks, such as thatillustrated inthe process of heading in Figure 7. There is a tendencyfor the recess forming punch to pull such short blanks out of the dieupon retraction of the punch, thus causing the machine to malfunction,and the slight bulging of the screw blank into the shallow annularrecess 31 of the die, during the headingoperation, serves to reduce thistendency of the blanksto be pulled from the die by the recess formingpunch.

Figures 8 and 9 illustrate dies of the so-called straight hole type,Figure 8 showing a die adapted for the production of blanks-of theprotruding head type While Figure9 relates to blanks of the countersunkhead type. Figure 10 illustrates a die for forming header point blanksof the protruding head type while Figure 11 illustrates a similar die ofthe countersunk head variety. The dies of Figures 8-l1 may be quicklyand conveniently produced by the This type of die illustrated inchamt'ered or tapered point serving as a lead to guide a threadedmachine screw into ready engagement in a tapped hole or as a pilot forsatisfactory use of'tapping screws. .Usually the diameterof the point ofthe blank is approximately of the larger diameter, and the angle of thetaper varies from approximately 42 to 15 depending on whether the screwblanks are to be chamfer point- It will be obvious thatin bobbing thistype of die, the diameter of the hole 'initiallydrilled in the blankmust approximate the smaller diameter of the finished screw blankwhereas the diameter of the portion 21 of the hob will be that of themain portion ofthe shank of the screw blank. Because of the wideditference in these two diameters, requiring drastic materialdisplacement, there is a definite limit in the distance which the hobcan be pressed into the die blank,

usually about-4 times the diameter of the portion 21 of the hob, and .inthe resulting length of the headed screw blank produced. This limitationis not a serious one, as there arecertain other factors inherent in thecold heading operation which limit the length of header point blankswhich can be produced. I

It has been found possible to hob dies for very short header point screwblanks from a solid die blank, such as that seen in Figure 12. Afterhobbing, such dies are drilled through to a diameter somewhat smallerthan the final point diameter following which this smaller hole can behobbed in the maner described for the straight hole dies to produce afinished die such as seen in Figure 13. Such secondary bobbing, however,is not essential since a drilled hole will adequately accommodate theknock-out pin of the heading machine.

Figures 14, and 16 illustrate dies of the extrusion type, formedaccording to the present invention. The die of Figure 14 has been formedwith the usual tapered portion joining the straight portion 36 with theconstricted extrusion choke 37, whereas the die of Figure 15 is formedto provide a connecting portion 40 of different form between thestraight portion 41 and the extrusion choke 42. The portion 40 isprovided with an inwardly concave longitudinal curvature, whichpossesses certain advantages in the case of extrusion dies. There isalso the possibility of such a corresponding rounded or convex shapebeing required in the finished screw, and one of the advantages of thepresent method of producing header dies lies in the possibility ofproducing screw blanks of such shape. No other method is known wherebythis internally curved condition may be produced in a header die, with asatisfactory finish, by the conventional methods. As illustrated inFigure 16, if the diameter of the shank portion of the die aperture issufficiently larger than that of the extruding choke, the resultantbulging of the portion 23 of the die forming hob will cause acorresponding annular concavity in the die which, in this case, willmerge with the concavity of the portion 40 as designed into the die toproduce the concavity 43 of Figure 16.

in all of the cases described above, the advantages of economy, speed ofproduction, accuracy, superior finish, longitudinal lay of the finish,and prevention of blank pullout, are inherent. In the case of extrudingdies, however, which are used principally to head alloy steel blanks foraircraft screws, it has been found virtually impossible to produceheader dies from the proper grade of tool steel by the conventionalmethods, with the result that dies used in this type of headingoperation gave a relatively unsatisfactory performance and were of veryshort useful life. Dies made according to the present invention, on theother hand, not only perform more satisfactorily and last much longer inthis service, but produce better screw blanks of the extruded typebecause the direction of the die finish is longitudinal, eliminating thedefects caused by the annular finishing marks of dies pro duced by theconventional methods.

Having thus described the invention, what is claimed as new and desiredto be secured by Letters Patent is:

1. Method of making header dies of cold heading machines comprisingpreparing an unhardened die blank, supporting said die blank with oneend and all lateral surfaces rigidly confined, and cold forming said dieblank under heavy pressure with a hardened and polished hob having aconfiguration substantiallycomplementary to the desired finished die,said hob having a body and a diepenetrating projection, the latterpenetrating the die blank in the forming step to produce a die aperturein which any irregularities of the walls extend longitudinally, said hobprojection having a reduced terminal portion end, said forming beingdone with sutficient pressure to cause annular elastic bulging of saidhob projection at a point near said terminal portion, withdrawing saidhob, finishing the other end of said die blank, and hardening saidblank.

2. In the method of claim 1, the step of pre-drilling the die blank toproduce an aperture of slightly smaller diameter than the desiredfinished diameter of the die aperture.

3. In the method of claim 1, the step of pre-drilling the die blank toproduce a through aperture of slightly smaller diameter than the desiredfinished diameter of the die aperture.

4. -In the method of claim 1, the step of drilling the formed die blankfrom the end opposite to that penetrated by said projection, to connectwith said aperture.

5. Method of making header dies of cold heading machines, comprisingpreparing a centrally bored, unhardened die blank, supporting said blankwith one end and all lateral surfaces rigidly confined, and cold formingsaid die blank with a hardened and polished hob having a configurationsubstantially complementary to the desired finished die, said hob havinga body and a central projection extending into the bore of said dieblank, said projection including an enlarged portion adjacent said body,having a transverse section of substantially greater diameter than saidcentral bore, a reduced terminal portion having a transverse section ofslightly greater diameter than said central bore, and an intermediateportion connecting said other portions, said forming being done withsufficient force to cause elastic bulging of said hob projection in theregion of said enlarged portion adjacent its junction with saidintermediate portion, withdrawing said hob, finishing the other end ofsaid die blank, and hardening said blank.

6. Method of making header dies of cold heading machines, comprisingpreparing a centrally bored, unhardened die blank, supporting said blankwith one end and all lateral surfaces rigidly confined, and cold formingsaid die blank with a hardened and polished hob having a configurationsubstantially complementary to the desired finished die, said hob havinga body and a central projection, the latter penetrating the die blank inthe forming step to produce a die aperture in which any irregularitiesof the walls extend longitudinally, said projection including anenlarged cylindrical portion adjacent said body, having a transversesection of substantially greater diameter than said central bore, areduced cylindrical terminal portion having a transverse section ofslightly greater diameter than said central bore, and a frustoconicalintermediate portion connecting said other portrons, said forming beingdone with sufiicient force to cause permanent deformation of said dieblank into the desired shape and compression and hardening of thesurfaces contacting said hob, withdrawing said hob, finislhinkg theother end of said die blank, and hardening said References Cited in thefile of this patent UNITED STATES PATENTS 2,014,698 Reilly Sept. 17,1935 2,066,372 Tomalis Jan. 5,' 1937 2,618,989 Cupler Nov. 25, 19522,638,019 Stellin May 12, 1953 2,699,693 Stellin Jan. 18, 1955

